XOR cypher function, type casting from ASCII help

[hybrid rock]

My goal is to make the following function:

char* EncryptXOR(char* hexString, char* key)

that takes a string of 32-bit hex and uses xor encryption on it using a 4-letter ASCII key. I'm not sure how to approach it besides converting the two to int, XORing, then converting the result back to ASCII. The last step I'm having trouble with because I would have to un-concatenate the result and convert each to the equivalent character.

I know there must be a more efficient way to turn ascii into an int, do something to it, and turn it back to ascii, I just can't find anything that works.

[dusty pelican]

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[pine rain]

a string of 32-bit hex
a what

[hybrid rock]

sorry, like "0000F000"

[pine rain]

oh i see

well

you loop over hexString and at the same time over key

for (int i = 0; i < strlen(hexString); i++) {
    /* do stuff with */ key[i % strlen(key)]
}

the i % len ensures that youre not accessing out of bounds

[hybrid rock]

thats for the encrypting part right

[pine rain]

for both

[hybrid rock]

how should i turn the key into an int tho

[pine rain]

why would you

[hybrid rock]

u can xor an int with a character?

[pine rain]

both hexString and key are chars

not ints

[hybrid rock]

oh

so u can xor 2 characters together?

[pine rain]

why wouldnt you be able to ?

it get implicitly converted to an int if you mean that

[hybrid rock]

so for that operation it would use the ascii values

[pine rain]

and then back to a char once you assign

char a = 123;
char b = 111;

char c = a ^ b;
^^^^^^   ^^^^^
char      int 

[hybrid rock]

oooo

[pine rain]

;compile

char a = 123;
char b = 111;
char c = a ^ b;
printf("%zu\n", sizeof(char));
printf("%zu\n", sizeof(int));
printf("%zu\n", sizeof(c));
printf("%zu\n", sizeof(a ^ b));

[storm atlas]

Program Output

1
4
1
4

nekrogenesis | 61ms | c | x86-64 gcc 13.2 | godbolt.org

[hybrid rock]

whats %zu?

[pine rain]

sizeof returns size_t and the correct format specifier for that type is zu

[hybrid rock]

oh ok

okok

hmm

char* EncryptXOR(char* hexString, char* key) {
    char* encryptedString = (char*)malloc(9); 
    encryptedString[8] = '\0';

    for (int i = 0; i < strlen(hexString); i++) {
    encryptedString[i] = hexString[i] ^ key[i % strlen(key)];
    }

    return encryptedString;
}

i have this but the output isnt matching the test cases still, is there anything obviously wrong

[pine rain]

dont hardcode sizes that are supposed to be variable

size_t len = strlen(hexstring);
char* encryptedString = malloc(len + 1); 
encryptedString[len] = '\0';

for (int i = 0; i < len; i++) {
    ...
}

[hybrid rock]

ooh thanks

its still not working but i'll work it out :(

thanks for your help

[dusty pelican]

Thank you and let us know if you have any more questions!

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